Modern cars also are loaded with logic circuits/mini-computing capability, and above-ground conditions where metal doesn't always meet metal, making for poor grounds. And, with transmitting thrown into the mix, it is always good to pursue the manufacturer via its help phone number (since the dealer service and parts deptartments don't have a clue). You want the factory recommendations for radio installations such as they provide to public service entities. There are tech sheets. Sometimes you have to push hard to get them, but it can/will save you a lot of headaches and maybe warranty considerations.
And, especially for transmit, I recommend RG-6X MM coax. The MM stands for marine-mobile and means a stronger shield and outer jacket to resist chafing and contamination.